Quartz particles are Certified Reference Materials useful as calibrants and reference materials for particle analysis instruments and techniques requiring samples with a wide size distribution. They are useful for evaluating laser diffraction and electrical resistance analyzers, and for calibrating sieve openings. These standards were prepared under the sponsorship of the Community Bureau of Reference (BCR), the standards bureau of the European Common Market, and executed by laboratories in Germany, Italy and the United Kingdom. Mined in Fruechen, West Germany, the quartz is mostly silicon dioxide with trace amounts of iron (Fe), titanium (Ti), sodium (Na) and calcium (Ca). The chemical composition was characterized by using hydrofluoric acid dissolution, then analysing the residue. Sodium and calcium contents were determined by flame photometry. Iron and titanium were determined using spectrophotometric techniques. Density was determined by pyknometer and is approximately 2.6 g/cm3. BCR 66, 67, 69 and 70 were calibrated by gravimetric sedimentation, and BCR 68 and 130 by a sieving technique. The samples were also analyzed by TEM, electrical sensing zone, sieving and several sedimentation methods. A continuum of the weight distribution is provided for each sample. Results and methods are summarized in two detailed reports: Certification Report on Reference Materials of Defined Particle Size for BCR 66 through 70, and Reference Materials of Defined Particle Size for BCR 130. Both reports are included with the kit. (We will also add the appropriate report to an order of any 6 or more individual items.) Each individual bottle of the quartz reference materials is accompanied by a Certificate of Measurement, which outlines measurement methods, chemical analysis data and instructions for use.